Nepenthes neoguineensis is a climbing plant. The stem is up to 6 mm thick and cylindrical to obtusely angular in cross section, especially in the upper part of the
internodes. Internodes are up to 4 cm long. Leaves are
chartaceous and
petiolate. The
lamina is
lanceolate and reaches 25 cm in length and 4.5 cm in width. It has an acute apex and is gradually or rather abruptly
attenuate towards the base. Three or four indistinct longitudinal veins are present on either side of the
midrib.
Pinnate veins ascend obliquely from the midrib and are irregularly
reticulate in the outer part of the lamina.
Tendrils are up to 4 mm thick and about as long as the lamina. Upper pitchers gradually arise from the ends of the tendrils, forming a 7 to 23 mm wide curve. They are
infundibulate in the lower part, somewhat
ventricose at two-fifths of their height, and widened towards the mouth. A pair of fringed wings (≤8 mm wide) runs down the entire length of the pitcher. The pitcher mouth is oblique and
acuminate towards the lid. The
peristome is cylindrical or flattened and up to 1.5 mm wide. The glandular region covers the lower third of the inner surface of the pitcher. The glands occur at a density of about 700 to 900 per square centimetre. The lid is
suborbicular,
truncate or slightly
emarginate, and rounded or slightly
cordate at the base. Round, depressed glands are present on the undersurface of the lid, being concentrated and increasing in size towards the middle. A flattened, unbranched
spur (≤3 mm long) is inserted at the base of the lid. The male
inflorescence is a long, cylindrical
panicle. The
peduncle reaches 12 cm in length and 4 mm in width. The
rachis is attenuate and up to 44 cm long.
Pedicels lack
bracteoles, reach 55 mm in length, and are one- to four-flowered.
Tepals are
orbicular-elliptical and around 4 mm long.
Stamens are about 4 mm long, including the
anthers. The female inflorescence is a panicle-like
raceme. The peduncle may be up to 15 cm long and 2.5 mm wide. The rachis is attenuate and reaches 20 cm in length. Pedicels are up to 35 mm long and most have
filiform bracteoles. They are one- to three-flowered. Tepals are oblong-lanceolate and approximately 4 mm long. The
ovary is sessile.
Nepenthes neoguineensis has a very sparse
indumentum. The stem is virtually
glabrous, as is the lamina. Tendrils are densely
hirsute when young, becoming only hairy near the pitcher or entirely glabrous when mature. Pitchers have a dense covering of
caducous stellate hairs. The exception is the spur, which has persistent stellate hairs. Inflorescences have a very dense indumentum of short, white or brownish stellate hairs. The pedicels, tepals and the ovary are very densely stellate-
tomentose. Lower pitchers range in colour from light green to dark purple throughout. Upper pitchers are generally yellowish-green, often with a darker peristome and bright red lid. Herbarium specimens are fallow-dun in colour. ==Ecology==